In the name of Allah, the Most Gracious and the Most Merciful.
According to Shafi’i scholars, it is a condition to say the niyyah daily.
However, if you fear of forgetting to say the niyyah, you may say it for the entire month but at the same time to say it daily as well. If you happened to forget, then having an intention to fast, your fast is still valid.
We hope that all our fastings will be accepted by Allah s.w.t.
Allah knows best.